Method and device for separating sheets from a stack

ABSTRACT

A method and a device for separating the sheets of a stack are described. At least one flexing device engages at the top sheet of the stack, tensioning or arching the edges of the top sheet. This creates a clearance between the top sheet and a second, lower sheet. A separating edge is inserted into said clearance so that the top sheet can be removed by a transport arrangement.

RELATED APPLICATION

[0001] This application claims priority to German patent application 101-47-410.5, filed Sep. 26, 2001, which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The invention relates to a method and a device to separate sheets from a stack.

BACKGROUND ART

[0003] Especially with office machines, such as printers, copiers, but also printing machines, etc., it is necessary to separate stacked single sheets, sets of sheets, transparencies or similar thin flat materials from the stack and transport them for further processing. In the following, the term “sheets” is used to represent all different types of sheet-shaped flat materials.

[0004] A number of methods are known to separate sheets from a stack. Some of these methods work dependably only within a relatively narrow range of sheet weights, types and surface conditions. For a particularly broad spectrum of sheets, i.e., paper of various weights, types and surface conditions, transparencies, etc., flexing the stack has proved to be a dependable method. A flexing effect is exerted on the top sheet of the stack in the direction of travel of the sheet. Said flexing effect causes the upper sheets of the stack to be fanned open like shingles, so that the top sheet can be separated and removed. However, said separation by flexing is too slow for many applications.

[0005] The embodiment of the invention was based on the problem to provide a method and a device to separate sheets from a stack, which works dependably and at a high separation speed with a broad spectrum of sheet types.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

[0006] The problem is solved in accordance with the invention with a method having the characteristics of claim 1 and/or with a device with the characteristics of claim 11.

[0007] Advantageous embodiments of the invention are listed in the respective dependent subclaims.

[0008] The essential idea of at least certain embodiments of the invention is to either tension or buckle the respective top sheet of a stack to create a clearance between the top sheet and the next sheet. The stack can be arranged concave, convex or flat. With a concave stack, the top sheet is tensioned in accordance with at least one embodiment of the invention, and with a convex or flat stack, the top sheet is arched. Even a very small tensioning or buckling of the top sheet will cause it to be lifted and separated from the second sheet below. To tension or arch the top sheet, a force directed transversely to the center axis of the sheet is exerted on the surface of the top sheet. To tension the top sheet of a concave stack, the force is directed outward. To arch the top sheet of a convex of flat stack, the force is directed inward. Said force can be generated in various ways, for example by friction. It is especially advantageous to generate said force with flexing. This makes the separation largely independent of the condition of the sheets so that the separation can be used successfully with a broad spectrum of sheet types.

[0009] In one embodiment of the invention, respective forces are exerted on both edges of the sheet in mirror symmetry. In this way, the sheet is tensioned or arched symmetrically to the center axis, and it is not displaced laterally against the stack during the tensioning.

[0010] In order to keep the top sheet, which was separated by the tensioning or arching, separate from the following second sheet of the stack, appropriate means of separation, for example in the form of a separating edge, are inserted between the top sheet and the second sheet. Preferably, said means of separation are inserted in the center area of the sheets, where the clearance between the tensioned or arched top sheet and the second sheet is the greatest.

[0011] The means of separation keep the top sheet separated from the stack so that it is free to be transported away from the stack.

[0012] The removal of the top sheet can be effected by means of transportation that engage at the top sheet in the area where said top sheet is tensioned or arched, and kept separate by the means of separation. In that case, the means of separation, such as the separating edge, can be used to press the top sheet against the means of transportation so that said means of transportation can take the top sheet and remove it. In this way, the entire top sheet can be removed from the stack before the means of tensioning or arching and separating the following sheet are again placed on the stack.

[0013] In another embodiment, the sheet is tensioned or arched at one of its ends while the means of transportation engage at the opposite end of the sheet. The means for tensioning or arching the sheet therefore can be already again placed on the second sheet of the stack as the upper sheet is being removed with said means for tensioning or arching, but has not yet been pulled completely from the stack. In this embodiment, the top sheet is kept separate from the second sheet during removal from the stack in that the means of separation exert pressure on the second sheet and hold it on the stack while the top sheet is being removed.

[0014] The invention is explained in greater detail in the following by means of an embodiment shown in the illustration.

[0015] Shown are:

[0016]FIG. 1 a front view of the concave stack of sheets,

[0017]FIG. 2 the device in the starting position, in vertical section along the center axis of the sheet,

[0018]FIG. 3 a top view of the device at the start of separation,

[0019]FIG. 4 a front view of the device during separation,

[0020]FIG. 5 a corresponding front view of the device after completion of the separation and during removal of the top sheet,

[0021]FIG. 6 a vertical section of the device in the position of FIG. 5,

[0022]FIG. 7 the removal of the top sheet, in vertical section,

[0023]FIG. 8 a top view of the device in the position of FIG. 7, and

[0024]FIG. 9 a second embodiment of the device in a representation corresponding to FIG. 6

[0025] In order to feed sheets to an office machine such as a printer or copier, said sheets are provided in a stack. The sheet stack 10 is held in a receptacle. In the shown embodiment, the receptacle is developed as support plate 12, on which the stack 10 is deposited. The support plate 12 is bent in the direction of the center axis of the stack of sheets, as is shown in the front view of FIG. 1. If the pages are sized DIN A4 and delivered to the office machine in longitudinal direction of the sheet, the bend of the support plate 12 runs in the center axis of the support plate 12. The angle of bend is approximately 160° to 175°. The stack 10 on the support plate 12 therefore has a slight concave arch, with the bending axis of said arch running parallel to the center axis of the sheet.

[0026] To separate the top sheet 14 from the stack 10 and deliver it to the office machine, the top sheet 14 is tensioned transversely to the axis of the concave arch in the manner described later on. To do so, the two longitudinal edges of the sheet 14 that are parallel to the axis of curvature are pulled apart so that said top sheet 14 is no longer arched, but is tensioned rectilinearly. For example, if the bending angle of the support plate 12 is 168° and the sheets of the stack 10 are DIN A4 sheets, it is sufficient to pull apart the two longitudinal edges of the top sheet 14 by approximately 0.45 millimeters respectively to lift off the top sheet 14 in its center area by approximately 1 centimeter from the following second sheet of the stack. It is obvious that this slight displacement of the lateral edges of the top sheet 14 can proceed very quickly, and the dependable flexing action in particular can effect this slight path of displacement at high speed.

[0027] This action is used in accordance with the invention in the following manner to separate the sheets from the stack 10.

[0028] A carriage 16 approaches the stack 10 at its concave front side. If only one single stack 10 is provided, the carriage 16 can be arranged at the front side of said stack to be vertically movable. If a multiple of stacks 10 is provided, the carriage 16 can be movable such that it makes a respective controlled approach to a selected stack 10.

[0029] The carriage 16 has means to tension the top sheet 14 of the stack 10. Said means are developed such that they engage at both sides of the center axis of the sheet at the surface of the top sheet 14 and displace the edges of the sheet away from the center axis of the sheet toward the outside. In the example of the embodiment, the means for tensioning the top sheet 14 are comprised of two flexing devices 18 that are placed on the surface of the sheet and engage at said surface of the sheet. The flexing devices 18 each have a continuous crawler belt 20 that is equipped with flexing rollers 22. The circulation plane of the crawler belt 20 runs vertically to the center axis of the sheet, with the lower stand side of the crawler belt 20, which is placed on the top sheet 14, running from the center axis of the sheet against the direction of the edges of the sheet. The crawler belts 20 are driven by means of a respective electrical motor 24 through a transmission 26. The flexing devices 18 are supported with spring load at the carriage 16. This is achieved preferably with a torsion bar spring 28, the center of which is supported like a balance beam at the carriage 16 to be pivoted therewith and supports on its two free ends the flexing devices 18. In this way, the two flexing devices 18 and their flexing rollers 22 are pressed to the surface of the top sheet 14 with precisely the same force symmetrically to the center axis of the sheet when the carriage 16 is lowered. The flexing rollers 22 thus flex the top sheet in its two peripheral areas with precisely the same flexing effect and thus displace the two edges of the sheets in mirror symmetry towards the outside. This prevents any travel of the top sheet 14 in the direction of one of the two sides.

[0030] Furthermore, separating means are arranged at the carriage 16. Said separating means are supposed to keep the top sheet 14, which was tensioned and thus lifted off the stack 10 in the aforementioned manner, separate from the second sheet of the stack. In the embodiment shown, said means of separation have a separating edge 30, which can be inserted from the face side of the stack 10 in the center area of the stack between the tensioned top sheet 14, which has been lifted off the stack, and the second sheet, which is on the stack 10. The displacement of the separating edge 30 is effected by an electrical motor 22 through a toothed rack 34. By means of said drive, the separating edge 30 can be displaced between a starting position, as it is shown in FIG. 2, and a driven-in position, as it is shown in FIG. 6. In the starting position, the separating edge 30 is outside of the face side of the stack 10, and in the driven-in position, the free end of the separating edge 30 engages in the stack 10.

[0031] Finally, a transport arrangement 36 is arranged at the carriage 16. The transport arrangement has the function of removing the top sheet 14, which was separated from the stack 10, from said stack 10 and transport it for further downstream processing.

[0032] In the shown embodiment, the transport arrangement 36 has a circulating friction-capable conveyer belt 40 that is driven by means of an electrical motor 38.

[0033] As indicated in FIG. 5, the images received at both the left and right eyes as indicated at 59 and 60, are then combined in the mind of the user as indicated at 64 to visualize the entire image of both the candle and its holder.

[0034] Referring now to FIG. 6, a vision therapy system 67 is illustrated and is constructed in accordance with yet another embodiment of the present convention. The system 67 includes an image 69 produced by a computer display 70. A pair of eyeglasses having a green lens 74 and a red lens 76 is similar to the pair of eyeglasses 21 of FIG. 1. The pair of eyeglasses 72 are worn by the user and are adapted to enable the user to play a game to amuse oneself while undergoing vision therapy.

[0035] The image 69 includes a green Christmas tree image 83 and a set of red ornament images 81 to be matched with a corresponding set of gray ornament images 83 disposed on the green background Christmas tree image 78. In this regard, the images on the computer display 70 may be produced by suitable computer software, and enable the user to move the red ornament images 81 to the corresponding positions of the gray ornament images 83 on the Christmas tree image 78.

[0036] The green lens 74 of the pair of eyeglasses 72 permit the right eye of the user to visualize the green Christmas tree image 78 and the red ornament images 81, but not the gray ornament images 83. In this regard, the green lens 74 imparts a green color component to the gray ornament images 83 so that they may not be distinguished from the green background provided by the green Christmas tree image 78. Thus, as indicated at 85, the resulting image at the right eye of the user is without the gray ornament images 83.

[0037] The described arrangement works in the following manner:

[0038] In idle condition, the arrangement is in the starting position shown in FIG. 2. The carriage 16 and the flexing devices 18 are elevated so that the flexing devices 18 are not in contact with the top sheet 14 of the stack 10. The separating edge 30 is in its starting position outside of the stack 10.

[0039] Upon an electronic starting command, the carriage 16 is first lowered relative to the stack 10 until the flexing rollers 22 of the two progressively spring-loaded flexing devices 18 rest on the top sheet 14 with slight pressure. This operates a sensor, which starts the electrical motors 24 of the flexing devices 18 so that the crawler belts 20 circulate and act on the edges of the top sheet 14 by means of the flexing rollers 22. In that way, the carriage 16 is driven progressively stronger against the stack 10 by means of the step motor that drives the carriage 16, so that the contact pressure of the flexing rollers 22 against the top sheet 14 is increased progressively until the top sheet 14 has been tensioned and lifted off the stack 10. The tensioning of the top sheet 14 operates an additional sensor, which reports that the required clearance between the top sheet 14 and the following second sheet of the stack 10 has been created. The flexing movement is indicated in FIG. 3 with arrows. FIG. 4 shows the lifting of the top sheet 14 by said flexing.

[0040] The sensor signal, which reports sufficient tensioning of the top sheet 14, operates the separating edge 30. Said operating edge is moved from its initial position shown in FIG. 2 against the face side of the stack 10, where it penetrates between the lifted off top sheet 14 and the following second sheet of the stack 10, as shown in FIG. 5 and 6. The inserted separating edge 30 then presses the top sheet 14 against the transport belt 40 of the transport arrangement 36. The carriage 16 is then lifted again in a controlled movement. This also lifts the flexing devices 18 from the top sheet 14, and said sheet is free for removal. Then the transport belt 40 can be operated again to remove the sheet.

[0041] After the top sheet 14 has been removed, the arrangement is returned to the initial position shown in FIG. 2 until the starting command for the removal of the next sheet is received.

[0042] The tensioning of the top sheet 14 due to the flexing effect of the flexing devices 18 is largely independent of the properties of the sheets so that the separation can be used simultaneously in the same way for sheets with varying strengths and qualities. Because the tensioning requires only a minimal displacement path of the edges of the top sheet 14, the separation can take place at high speed.

[0043] In the embodiment of the FIGS. 2 to 8 described above, the flexing devices 18 can be again placed on the stack 10 for separating the next sheet only if the preceding sheet under the flexing devices 18 has been removed completely. In another embodiment of the invention shown in FIG. 9, this is prevented in that the transport arrangement for removing the separated top sheet from the stack is arranged not at the face side of the stack 10, where the flexing devices 18 engage, but at the opposite face site.

[0044] In said embodiment, the top sheet 14 is not removed at the face edge of the stack where the transport arrangement 36 engages. Therefore, in said arrangement, the separating edge 30 is lowered on the stack after it has been inserted between the tensioned and lifted off top sheet 14 and the next sheet of the stack 10, and presses the following second sheet on the stack 10 to keep said sheet firmly in place while the top sheet 14 is being removed. Preferably, the separating edge 30 has a friction lining on its underside for this purpose.

[0045] In this embodiment, the carriage 16 with the flexing devices 18 and the separating edge 30 can be suitably tilted around a horizontal axis 42 that is parallel to the face edge of the stack 10. After the separating edge 30 has been inserted, the carriage 16 is lowered further. In that way, the separating edge 30 presses the second sheet on the stack with a cam lobe 44 arranged at its underside. When the carriage 16 is lowered further, said stack is therefore tilted, so that the flexing devices 18 are lifted from the top sheet. Thus, the top sheet is free for removal by the transport arrangement 36 while the second sheet is reliably held in place.

[0046] Because in said embodiment the sheet is removed from the stack in opposite direction, its face edge is immediately removed under the flexing devices 18 so that the flexing devices 18 can be placed on the next sheet again even before the top sheet has been removed completely from the stack 10. This allows for the separation of the stack in quick succession.

[0047] In another embodiment of the invention, which is not shown in illustration, the stack is arranged convex or flat, and only one flexing unit is provided. Said flexing unit slides the top sheet against a firm lateral stop, which is provided anyway for the stacking of the sheets. In that way, said top sheet is arched and removed from the next sheet of the stack.

[0048] List of reference symbols 10 stack 12 support plate 14 top sheet 16 carriage 18 flexing devices 20 crawler belt 22 flexing rollers 24 electrical motor 26 transmission 28 torsion bar spring 30 separating edge 32 electrical motor 34 toothed rack 36 transport arrangement 38 electrical motor 40 transport belt 42 tilting axis 44 cam lobe 

What is claimed is:
 1. Method for separating sheets, from a stack with the following steps: tensioning the surface of the top sheet of the stack transversely to the center axis of the sheet, causing it to be lifted from the second sheet of the stack; maintaining the top sheet and the following second sheet separate with the clearance in their center areas; and removing the top sheet from the stack.
 2. Method in accordance with claim 1, wherein the stack is held concave with an axis of deflection that is parallel to the center axis of the sheet, and that the top sheet is tensioned by forces directed away from the center axis of said sheet in mirror symmetry.
 3. Method in accordance with claim 1, wherein the stack is held convex or flat with a axis of deflection that is parallel to a center axis of the sheet, and that the top sheet is arched by a flexing movement directed to toward the center of the axis of the sheet.
 4. Method in accordance with claim 3, wherein a force acting on the top sheet is sliding said top sheet against a firm lateral stop, thereby arching said sheet.
 5. Method in accordance with claim 3, wherein the top sheet is arched by forces directed in mirror symmetry toward the center axis of the sheet.
 6. Method in accordance with one of the claims 1 to 5, wherein the force acting on the top sheet is generated by a flexing movement.
 7. Method in accordance with one of the claims 1 to 6, wherein the top sheet, which was separated from the second sheet, is held in lifted off position to be removed from the stack.
 8. Method in accordance with one of the claims 1 to 6, wherein the second sheet is held on the stack for the removal of the separated top sheet.
 9. Method in accordance with one of the claims 1 to 8, wherein the top sheet of the stack is captured with a contact pressure that increases progressively until the top sheet is lifted from the second sheet.
 10. Method in accordance with claim 9, wherein the contact pressure at first starts at a low value and is increased until a sensor recognizes that the top sheet has been lifted from the second sheet.
 11. Device for separating sheets from a stack, comprising: means for flexing or arching the top sheet of the stack, which engage at the surface of the top sheet and exert a force acting on the edges of the sheets transversely to the center axis of the sheet, separating means for moving between the second sheet of the stack and the top sheet lifted off from said second sheet, and with transport means that remove the top sheet separated from the second sheet from the stack.
 12. Device in accordance with claim 11, wherein a receptor for the stack holds said stack with an axis of bend that is parallel to a center axis of a sheet.
 13. Device in accordance with claim 12 or 13, wherein the means for tensioning or arching the top sheet have flexing devices.
 14. Device in accordance with claim 13, wherein two flexing devices are arranged in mirror symmetry to the center axis of the sheet and are spring-supported with equal contact pressure.
 15. Device in accordance with claim 13 or 14, wherein the flexing devices have circulating conveyer belts equipped with flexing rollers.
 16. Device in accordance with one of the claims 11 to 15, wherein the means for tensioning the top sheet can be placed on the top sheet with a contact pressure that can be increased progressively from a lower value until the top sheet has been removed from the second sheet of the stack.
 17. Device in accordance with claim 16, wherein a sensor detects the removal of the top sheet.
 18. Device in accordance with claim 16, wherein the contact pressure is increased by means of a step motor.
 19. Device in accordance with one of the claims 11 to 18, wherein the means of separation have a separating edge that can be moved between an initial position in front of the face edge of the stack and a driven-in position in the stack.
 20. Device in accordance with one of the claims 11 to 19, wherein the means for tensioning or arching the top sheet are supported at a carriage that can be driven to the stack.
 21. Device in accordance with claim 20, wherein the means of separation are supported at said carriage.
 22. Device in accordance with one of the claims 11 to 21, wherein the transport means are arranged at the face side of the stack, where the means for tensioning or arching the top sheet are arranged.
 23. Device in accordance with claim 22, wherein the means of separation hold the separated top sheet in contact with the transport means.
 24. Device in accordance with one of the claims 11 to 21, wherein the transport means are arranged at the face side of the stack, which is opposite the means for tensioning or arching the top sheet.
 25. Device in accordance with claim 24, wherein the means of separation moved between the top sheet and the second sheet of the stack press and hold the second sheet against the stack while the transport means engage at the top sheet. 